In the majority of angiosperm species, plastids and mitochondria, the DNA-containing cytoplasmic organelles, are inherited maternally. Even in plants with strict maternal inheritance, plastid transmission has been observed to be exceptional. Our goal was to detect rare plastid leakage via pollen in Nicotiana sylvestris and see if pollen transmission of plastids results in paternal mitochondria co-transmission. We used N. sylvestris plants with transgenic, selectable plastids and wild-type mitochondria as father plants. We used N. sylvestris plants with Nicotiana undulata cytoplasm as mother plants, including the CMS-92 mitochondria that cause cytoplasmic male sterility (CMS) through the homeotic transformation of the stamens. We found exceptional paternal plastid DNA in about 0.002 percent of N. sylvestris seedlings. However, we found no paternal mitochondrial DNA in any of the six plastid-transmission lines, implying that the cytoplasmic organelles are transmitted independently via pollen. We obtained eight fertile plastid transmission lines from fertile N. sylvestris mothers that did not transmit their plastids via pollen at higher frequencies than their fathers. We discuss the implications of cytoplasmic phylogenies for transgene containment and plant evolutionary histories.

Inheritance of Plastids

Plastids are cytoplasmic organelles that contain DNA and duplicate themselves independently of nuclear genes during mitosis and are distributed more or less equally to daughter cells. Correns (1909) discovered for the first time that plastids could be transmitted to offspring through the egg cytoplasm while studying leaf pigmentation in Mirabilis Jalapa.

The cytoplasm of the zygote in a variegated strain of Mirabilis contains both green and colourless plastids. These plastids are unequally distributed during cell division in the zygote to form the embryo. When such an embryo germinates, it produces a variegated plant with three types of branches: those with green foliage, those with colourless foliage, and those with variegated (green and white) foliage.

It was discovered that seeds produced by green branches gave rise to only green plants, while seeds produced by colourless branches produced colourless seedlings that did not survive due to a lack of chlorophyll. Seeds from the variegated branch, on the other hand, could produce three types of plants: plants with green, colourless, or variegated branches.

Genetics of Plastids

Many small cytoplasmic bodies known as plastids are found in the cytoplasm of plant cells. These plastids are classified into several types, including chloroplast, leucoplast, chromoplast, and others. Plastids develop from smaller particles found in the egg cytoplasm called proplastids. They reproduce independently of other cell parts through the division of self-duplication.

Plastid characteristics are inherited from the female parent in the majority of cases, but in some cases, a few characteristics are inherited from the male parent as well. Plant variegation is one of the most common examples of plastid inheritance. Some plant organs, such as the leaves, may have green and white patches or green, yellow, white, or pink spots when variegated.

These varying-colour spots reveal differences in the types of plastid. Although many plant variations are known to be governed by ordinary Mendelian genes (i.e., nuclear genes), there are a few known cases that show a largely maternal type of inheritance. In these cases, inheritance is determined by the nature of the plastids.

Carl Correns (1909) reported on a case of maternal transmission in Mirabilis jalapa (four-o’clock plant). These variegated plants’ blotchy or spotted leaves have patches of green and white tissue, but some branches have only green leaves and others only white leaves. Flowers appear on all types of branches and can be cross-pollinated in a variety of ways.

Plastid Inheritance in Mirabilis

• Plastid inheritance refers to the transmission of plastid characteristics through plasma genes found in plastids.
• C. Corens (1908) first described plastid inheritance in the four o’clock plant, Mirabilis jalapa.
• Mirabilis jalapa leaves can be green, white, or variegated, and some branches have only green, white, or variegated leaves. The presence of white or yellow spots of varying size on the green background of leaves is referred to as variegation.
• Some environmental factors, some nuclear genes, and in some cases plasma genes can cause variation.
• Uniparental transmission is the name given to this phenomenon. Again, sex linkage cannot explain the results of Mirabilis jalapa crosses.
• The inheritance of different leaf colours in Mirabilis jalapa could be explained if the plastids are somehow autonomous and are never passed down through male parents. To be genetically autonomous, an organelle must have its genetic determinants that are responsible for its phenotype.

• Because the egg contributes the majority of the cytoplasm containing many plastids and the male gametes contribute a negligible amount of cytoplasm, plastids present in the cytoplasm of the egg are responsible for the appearance of maternal colour in the offspring and the failure of the male plant to transmit its colour to offspring is the reason.
• Green, white, and variegated progeny are recovered in varying proportions in the offspring of variegated female parents. The variegated parent gives birth to three types of eggs: those with colourless plastids, those with only green plastids, and those with both chloroplasts and the leucoplast.
• As a result, zygotes derived from these three types of egg cells will produce green, white, and variegated offspring.

Inheritance of Lojap Trait in Maize

• Iojap is a trait in maize plants that produce green and white striped leaves. When present in a homozygous state, this trait is controlled by a recessive chromosomal gene (ij). The name iojap is a combination of ‘Iowa’ state (USA), the source of the maize strain, and japonica, the name of a stripped variety.
• When a normal plant with green leaves is crossed with an ioja parent, the offspring will have green leaves. When a reciprocal cross is made between a regular green plant (used as the male) and an iojap plant (used as the female).
• The green and white striped trait of leaf in iojap plants is inherited from the female parent due to maternal inheritance. It appears that iojap plants have two types of plastids: normal green plastids and abnormal iojap plastids.

• Plastids are randomly distributed in egg cells during their formation. If the egg cell receives normal green plastids, it will produce green-leaved plants regardless of which plant served as the pollen parent. If the egg cell receives abnormally colourless plastids, it will produce white-leaved plants. Plants with green and white striped leaves will be produced if the egg cell receives both green and abnormal plastids.
• Green males do not affect progeny, according to this backcross experiment. Two hypotheses have been proposed to explain the emergence of the iojap trait. According to one theory, abnormal plastids are caused by frequent mutations in the chloroplast genome.
• Another theory proposes that certain cytoplasmic elements other than chloroplast mutation cause chloroplast bleaching. It’s also possible that a nuclear gene regulates the formation of abnormal plastids in the cytoplasm. As a result, this type of inheritance represents a state of inaction between nuclear and cytoplasmic inheritance.

Conclusion

In the majority of angiosperm species, plastids and mitochondria, the DNA-containing cytoplasmic organelles, are inherited maternally. Even in plants with strict maternal inheritance, plastid transmission has been observed to be exceptional. Our goal was to detect rare plastid leakage via pollen in Nicotiana sylvestris and see if pollen transmission of plastids results in paternal mitochondria co-transmission. Plastids are cytoplasmic organelles that contain DNA and duplicate themselves independently of nuclear genes during mitosis and are distributed more or less equally to daughter cells. It was discovered that seeds produced by green branches gave rise to only green plants, while seeds produced by colourless branches produced colourless seedlings that did not survive due to a lack of chlorophyll. These varying-colour spots reveal differences in the types of plastid. Although many plant variations are known to be governed by ordinary Mendelian genes (i.e., nuclear genes), there are a few known cases that show a largely maternal type of inheritance. Plastid inheritance refers to the transmission of plastid characteristics through plasma genes found in plastids. When a normal plant with green leaves is crossed with an ioja parent, the offspring will have green leaves. When a reciprocal cross is made between a regular green plant (used as the male) and an iojap plant (used as the female).